A magnetic recording system widely used for recording television video and audio signals and used also for digital signals, is called the quadraplex system and it involves a magnetic tape about two inches wide which is driven past a transversely rotating headwheel carrying four equally-spaced magnetic heads. The heads move across the tape at right angles with the direction of linear movement of the tape, and each recorded track or path on the tape is at an angle .theta. on the tape with the direction of linear movement of the tape. The angle .theta. depends on the speed each head goes transversely across the tape relative to the linear speed of the tape. The transverse and linear speeds used for recording are used also for playback to insure that the heads will follow the recorded tracks at the angle .theta..
It is sometimes very desirable, particularly with digital signals, to be able to record the signals at one speed and play back the signals at another higher or lower speed.